1. Field of the Invention
This invention relates to a packaging material for photosensitive materials for photographic purpose.
2. Description of Prior Art
Various types of packaging materials for photographic photosensitive materials have widely been put to practical use, and various properties are required according to their uses.
As the packaging materials for photographic photosensitive materials, it is necessary to have various properties such as light-shielding, gas barrier, moistureproofness, antistatic property, rigidity, physical strengths such as breaking strength, tear strength, impact puncture strength, Gelbo test strength and wear resistance, heat sealing properties such as heat seal strength, cut-seal ability, hot tack properties (hot-seal ability) and seal ability of contraries, flatness, slipping character and the like. The cut-seal ability is the suitability for fusing seal. In this sealing method, the hot plate for press is changed to a knife-shaped, and melting adhesion and cutting simultaneously occur.
Generally, it is difficult to satisfy these properties by a single material. Therefore, a single layer film of a high-pressure low-density polyethylene (LDPE) kneaded with carbon black or a pigment, and a composite laminated film composed of a LDPE film and a flexible sheet such as paper, aluminum foil or cellophane, etc. have been employed. An example of the conventional packaging film is shown in FIG. 17. This film is the most fundamental single-layer packaging material consisting of a light-shielding LDPE film layer 22. Another example of the conventional packaging film is shown in FIG. 18. This film was used for packaging a product which particularly requires moistureproofness, and it is composed of a light-shielding LDPE film layer 22, a light-shielding metal foil layer 6 laminated on it through an adhesive layer 8, and a flexible sheet layer 5 laminated thereupon through an adhesive layer 8. Still another example of the conventional packaging film is shown in FIG. 19. This film was used as inner sheet of double-sheet gusset bag for packaging color photographic printing paper, and it is composed of a light-shielding LDPE film layer 22, a light-shielding metal foil layer 6, a flexible sheet layer 5, and a light-shielding LDPE film layer 22. They are laminated in that order, and an adhesive layer 8 is provided between each layers.
on the other hand, the present inventor has continued to investigate various packaging materials mainly for photographic photosensitive materials including the packaging materials of FIGS. 20-22. The packaging material of FIG. 20 consists of a metal foil layer 6 and two light-shielding L-LDPE film layers 16, 16 laminated on both sides of the metal foil layer each through an adhesive layer 8. The packaging material of FIG. 21 consists of a metal foil layer 6 and two light-shielding uniaxially stretched films 24, 24 laminated on both sides of the metal foil layer each through an adhesive layer 8. The molecular orientation axes of the stretched films are located so as to cross each other in order to raise physical strength. This packaging material is disclosed in U.S. Pat. No. 4,331,725. With respect to the packaging material containing a low-pressure linear low-density polyethylene (L-LDPE), a packaging material comprising at least one light-shielding film layer of polyethylene polymer of which more than 50 wt.% is L-LDPE and containing more than 1 wt.% of a light-shielding material has been disclosed (U.S. Pat. No. 4,452,846). The packaging material of FIG. 22 is the same as the packaging material of FIG. 18 except that a light-shielding L-LDPE film layer 16 is employed instead of the light-shielding LDPE film layer 22.
Physical properties of the conventional laminated films are not enough, and during packaging, the films were sometimes torn or punctured or were sometimes separated upon heat sealing of the films. In addition, when a large amount of a light-shielding material such as carbon black is added, physical strength as well as moistureproofness of the film is lowered. Then, the amount was set about 3 wt.%, and thickness of the film was more than 70 .mu.m. As a result, the film was stiff, and working efficiency of the packaging process was adversely influenced. The cost of packaging was also expensive.
In the case of the laminated film disclosed in the specification of U.S. Pat. No. 4,331,725, heat sealing properties are not superior because of using uniaxially stretched high-density polyethylene film, and problems in sealing occasionally happened in packaging processes. In the case of cross-laminated films where two uniaxially stretched films were directly laminated so as to cross each other without laminating an aluminum foil, when a photosensitive material was packaged in a gusset bag, pinholes were appreciably formed at its gusset portion.
By employing L-LDPE resin for the packaging material, physical strength such as tear strength and Gelbo test strength is increased and the blending amount of a light-shielding material can be increased. However, when the thickness of the film was increased, moldability as well as appearance decreases, and moreover, the surface of the film becomes slippery.
Generally, since water absorbability of carbon black is large which can lead to inferior moistureproofness, the film blended with carbon black was made thicker, or an aluminum foil layer or a metallized film layer was further laminated.
In the case of the packaging material for photographic photosensitive materials, packaging operations are carried out under a safe light which does not adversely influence the photosensitive materials. Then, it is preferable that the right side and the reverse side of this packaging material can easily be discriminated under the safe light and that light-shielding and heat resistance can be secured by this packaging material without increasing the thickness.
Particularly, as the packaging materials for X-ray films for dental use, as the packaging materials for radiograph films for detecting radiation exposure of a person who treats radioactive materials (badge film) and as the packaging materials for vacuum packaging of the X-ray films described in Japanese Patent KOKOKU No. 55-24089, the development of simple films capable of satisfying all properties required as the above packaging materials has been desired.